[R-390] How are your knobs ?

[Charles Steinmetz]

Dave wrote:

>Where do we get this 'metal glue'?

The OP said he used some version of cyanoacrylate ("super 
glue").  There are many versions -- every hobby store and machine 
supply has lots of them.  Choose by (i) substrates (get one for metal 
to metal bonding), (ii) the gap (that you will have between bushing 
and knob), and (iii) working time.  Most manufacturers publish 
detailed brochures aimed at getting you to the right choice, and they 
also have help lines you can call and someone will tell you what to 
get.  You may need to apply an accelerator before the adhesive.

Barry wrote:

>think they're referring to a product similar to JB Weld

JB Weld is epoxy.  Very good epoxy, as is West System epoxy.  Either 
of these would be a fine choice (I'm more familiar with epoxies than 
cyanoacrylates, so I'd probably gravitate to one of these if I didn't 
have help choosing a cyanoacrylate.  If the clearance is tight, you 
may want to thin the mixed epoxy with a little acetone to make sure 
it wets the whole bond surface (but don't go crazy with the thinning).

For either adhesive, you want the parts scrupulously clean.  I'd 
probably drop the knob and bushing into a can and cover them with 
acetone, let them sit a day or two, scrub the contact surfaces well 
with a stiff brush (a brand new .45 caliber bore brush should be 
great for the knob), then change the acetone and let them sit another 
day.  NB: acetone may remove the knob finish.

Epoxy would benefit from some "tooth" on the bonding surfaces (40 
grit sandpaper -- to do the bore, put a split into the end of a dowel 
and insert a strip of sandpaper).  I don't think cyanoacrylates need 
that much tooth, but do what the manufacturer suggests.

Best regards,

Charles